AN OCEAN OF AZURE
“The boom of the waves on the shingle.”--LEWIS MORRIS.
“Roll on, thou deep and dark-blue Ocean, roll!”--BYRON.
Not that the Ocean is always and everywhere blue. In a certain “arm of
the sea,” the Bristol Channel, it is commonly any tint that you please
rather than blue--brown, green, yellow, chocolate, only not the colour
that we love. If by chance it dons for a few hours a robe of azure,
that robe is merely a passing loan from the sky. And in dull weather it
can only be described as a huge puddle of muddy liquid.
People often grow to like best that to which they are accustomed. A
lady, who had spent most of her life on the borders of that brown
Channel, once assured me that she infinitely preferred it to the “deep
blue sea.” She had been to stay by the latter, and had found its
monotony of tint so uninteresting that she was charmed to get back to
her old friend.
Tastes differ, certainly. Not many would agree with her. Yet it is a
fact that the great Turner went to the Bristol Channel, with all its
mud, for many of his marvellous sea and cloud effects.
“Deeply, darkly, beautifully blue,” sang Byron of the ocean, and he
sang truly, even though the ocean itself, putting aside the Bristol
Channel, is not always and uniformly azure. Near land the tint is often
greenish. Sometimes it is pure green. Often it is a pale and watery
blue. At other times we have a leaden grey. The genuine ocean-blue,
which resembles nothing else on Earth, can seldom be enjoyed till one
gets on really deep water, far from land. Or--till one is looking at
the Mediterranean.
Why should the sea be blue? And why should the sky be blue? For the
matter of that, why should anything be blue? What do we mean by
colour?--whether blue or green, red or yellow?
We mean that particular tint--or sensation--which the object in
question causes us to see--or feel. The object receives sunlight,
and reflects it to our eyes. And since sunlight is white or
yellowish-white, one might expect that everything we look upon would
appear to us white or yellowish-white.
But everything does not. And the reason is that a ray of sunlight is
really a bundle of lesser rays, each of which has its own colour. If
a ray of light is made to pass through a prism, these lesser sub-rays
are spread out upon wall or floor, always in the same order, from
violet at one end to red at the other end. Light is believed to be due
to enormous numbers of most minute wavelets; and for each colour the
wavelets have a definite but different size. They are smallest at the
violet end, and largest at the red end.
Now when a ray of sunlight falls upon anything--leaf or flower, earth
or water--some of the sub-rays are absorbed or taken in, and some are
rejected or refused admission. A healthy leaf, for instance, absorbs
the red, the yellow, the blue, the violet, and refuses the green, which
is therefore thrown back from the leaf-surface to our eyes, making it
green to us. A ripe tomato absorbs the yellow and green, the blue and
violet, and reflects the red. A lump of blacklead absorbs greedily all
the rays, reflecting none, and so to our eyes it is black or without
colour. The petals of a white rose, on the contrary, absorb so little
colour of any kind, that practically the entire ray is sent again to us
as white light.
If this is the manner in which the ocean is blue, it means that
sea-water, and indeed water generally, must in itself be actually blue,
as a cake of ultramarine, a sapphire, a corn-flower, a forget-me-not,
are blue.
Could that be the case? For a long while men decisively answered--No.
Everybody knew that water was colourless, so the idea was flung aside
as impossible. Another explanation came up instead.
The sea is full of fine dust; and it was suggested that, as vast
multitudes of these floating dust-particles are exceedingly small, they
might be able to reflect only the smaller blue light-waves, and not
the larger yellow or the still larger red waves. Thus the sea would
naturally seem to be blue.
After much discussion, careful experiments were made. Different objects
were lowered to various depths, and the effect upon their colouring was
noted. The outcome of these and other tests went far to prove that the
old certainty was wrong, and that water is in itself blue.
Somebody may feel inclined to protest. “Water blue! But that is out of
the question. I have good sight, and I assure you there isn’t the least
sign of colour in water. Not the faintest. If you dip a bucket in the
sea, you will see for yourself.”
Yet all the while the colour may be there, actually existent, though
not to be detected by your eyes or mine in a pailful.
A short time ago I had to buy a piece of lace; and my intention was to
choose a pale straw or deep cream. The lace was wound in many folds
round a large cardboard, and it seemed to be exactly the right hue--a
rich yellow-cream, almost butter colour. Without further demur, I
ordered about a yard to be cut off.
On reaching home, I found myself in possession of a piece of wide
dead-white lace--or all but dead-white. It was actually a very pale
cream; and when a great many folds lay one over another the combined
effect was rich and yellow. But a single thickness of the material
showed no colouring.
The same may be seen with a single piece of very pale blue muslin.
It will appear to be white. But yards upon yards of the same, folded
together, will become quite a deep blue.
A single thin layer of ocean-water, in like manner, has too faint a hue
to be visible to ordinary eyesight. It is only when layers are piled
upon layers that the blue becomes distinct; and the deeper the water,
the deeper generally will be the colour. Some yards of water-thickness
may be said to correspond to a single thickness of lace or muslin.
While, however, we may say with tolerable confidence that the blue
of the ocean is a “True Blue,” this alone will not explain all the
varieties of tinting, seen at different times and in different places.
Sea-water is sometimes a rich profound blue, and sometimes a pale
sickly blue. It is sometimes dull, sometimes brilliant. It is sometimes
green, and sometimes almost black. For these variations, even while
accepting the new explanation, it has been found needful to revert to
the old theory in quest of added help. The sea is blue, because it
really and truly _is_ blue. But that is not all. It is a deeper or less
deep blue, a duller or brighter blue, a greenish blue or even a dull
yellow, because of the vast supplies of dust floating in it.
The Mediterranean was particularly examined, on account of its
remarkable depth and brilliancy of colouring; and it was found to be
exceptionally laden with dust, both fine and coarse, brought from land
by innumerable rivers, and also pounded by breaking waves on the long
surrounding coast-lines.
Such floating particles, at all events the bigger ones, are no longer
supposed, as once they were, to reflect only the tiny blue light-waves.
On the contrary, they are believed to reflect all the waves of light
indiscriminately, whether large or small; while the sea, by virtue of
its own power as a Blue material, captures all those reflected waves
except the blue, and allows the latter alone to reach our eyes.
Near British shores the water has often a strongly green tint; and this
may be due in part to floating particles of sand. The yellow of the
sand, combining with the blue of the water, would naturally form green.
Possibly also the sea, near shore, is sometimes affected in colour by
floating sea-weeds, green-tinted.
The blue of the sky is often reflected on the sea-surface, and
sometimes so powerfully as to overcome the real ocean-colour. One
hardly understands how intense such a sky-reflection may be, until one
has watched the whole sea transformed into glowing crimson or gold from
a radiant sunset.
Much the same perplexity has been felt about the blue colour of air,
as about the blue colour of the ocean; and much the same course of
explanation has been followed. Its blueness was long maintained to be
due only or mainly to the “scattering of sunlight” by infinite numbers
of floating dust-specks, which also serve to account for the golden
and crimson tints of sunset. It now appears that oxygen, an important
element in the atmosphere, has a faint blue tint of its own, like
water, which at least helps to answer for the blue of the air.
We may therefore say of Water that it is believed to be transparently
and intrinsically blue; and that its colour, though not actually due to
floating specks of dust and other impurities, is a good deal affected
by them. Such materials in the Ocean help to modify its colouring,
sometimes deepening it, sometimes adding to its brilliance, sometimes
deadening its brightness, sometimes turning it green or yellow.
Careful observation has also shown that, when water is especially free
from dust-specks, it is of a darker and duller hue than when they are
present in large quantities to capture and reflect the sunbeams.